INVESTIGADORES
PEREZ Hugo Alejandro
congresos y reuniones científicas
Título:
Energy and charge-transfer quenching of flavins in AOT-reversed micelles solutions.
Autor/es:
HUGO A. PÉREZ, LORENA VALLE, FAUSTINO E. MORÁN VIEYRA Y CLAUDIO D. BORSARELLI
Lugar:
Cordoba
Reunión:
Congreso; XI ELAFOT; 2012
Resumen:
Flavins are
widely distributed in the biosphere, serve as cofactors in redox proteins and
are commonly applied photosensitizers [[i]].
Riboflavin (RF), present in free form or as flavin mononucleotide (FMN) and
flavin adenine dinucleotide (FAD) in cells, is an important and efficient
endogenous cellular photosensitizer [[ii]].
The triplet state of a flavin can be quenched by oxygen and a variety of
electron donors, e.g. ascorbic acid, amines or amino acids, e.g. tyrosine or
tryptophan [1].
We have
studied RF triplet excited state (3RF*) quenching by tryptophan and
molecular oxygen in (AOT)-iso-octane-water
reverse micelles by laser flash photolysis (LFP) with excitation at 355 nm.
The 3RF*
quenching efficiency (hq) by
tryptophan is governed by the local concentration of the species at the
interface of the micelle, and also by fluidity and water content. The presence
of neutral radical of tryptophan (TrN·) was confirmed by two structureless bands located
around 510 and 330 nm, which demostrated an electron transfer quenching mechanism
[[iii]].
On the other hand,
the deactivation of 3RF* by molecular oxygen showed that hq decreases slightly with
the water content of the micelle, that is in agreement with RF location on the micelar
structure [[iv]].
The high increment of quenching efficient at low internal oxygen micelar
concentration is explained by the large constant of quenching (kq ca. 109 M-1
s-1).
[i] H. Gorner. Oxygen uptake after electrón transfer from amines, amino
acids and ascorbic acid to triplet flavins in air ? saturated aqueous solution.
J. Photochem. Photobiol. B. 87, 73 ? 80 (2007).
[ii] L. Chang- Yuan, L.
Yan- Yun. Electron transfer oxidation of tryptophan and tyrosine
by triplet states and oxidized radicals of flavin sensitizers: a laser flash
photolysis study. Biochim. Biophys. Acta. 1571, 71 ? 76 (2002).
[iii] T.B. Melø, M.A. Ionescu, G.W. Haggquist, K.R. Naqvi. Hydrogen
abstraction by triplet flavins. I: time-resolved multi-channel absorption
spectra of flash-irradiated
riboflavin solutions in water. Spectrochimica.
A. 55, 2299 ? 2307 (1999).
[iv] L. Valle, F.E. Morán Vieyra, C.D. Borsarelli. Hydrogen-bonding
modulation of excitated-state properties of flavins in a model of aqueous
confined environment. Photochem. Photobiol.
Sci. 11, 1051-1061 (2012).